Tumwater Water Hardness & Quality Report (2026)

Tumwater, Washington, in Thurston County — a Thurston County city adjacent to Olympia (the state capital) at the southern tip of Puget Sound, the site of Tumwater Falls on the Deschutes River — receives its municipal water from the City of Tumwater Water Division, drawing from the Deschutes River or local Thurston County groundwater wells in the Puget Trough.

The very soft 47 mg/L hardness and very low TDS of 98.9 mg/L reflect the Deschutes River and Thurston County's Puget Trough character — similar to the Olympia-Lacey area supply. The Deschutes River drains the Black Hills of Thurston County (Eocene Crescent Formation basalt and andesite — insoluble volcanic ocean floor basalt), the western Cascades foothills, and the Puget Trough glaciofluvial outwash. All source materials are insoluble volcanic silicate, producing the characteristically very soft water of the southern Puget Sound corridor.

At 47 mg/L, Tumwater's water is very soft — essentially no scale forms, soap lathers abundantly, and appliances maintain excellent efficiency. Annual descaling is sufficient. The PFAS level of 2.4 ppt is excellent — reflecting the protected Deschutes River watershed and the relatively limited direct PFAS military-industrial sources in the south Thurston County supply area (lower than the Joint Base Lewis-McChord zone in Pierce County).